Composite electrode for a photo-rechargeable storage battery

ABSTRACT

A composite electrode for a photo-rechargeable storage battery includes a filter paper of glass fiber as a base material; a polypyrrole film coated on a surface of the filter paper to provide a conductive polymer; and a gel of polytungustic acid provided on the polypyrrole film in the form of a cluster to provide a photo-catalytic property. The polypyrrole film may be vapor phase polymerized and coated onto a surface of the filter paper and the gel of polytungustic acid may be vapor phase coated onto the polypyrrole film in the form of a cluster. Thus, all electrode manufacturing steps can be carried out in the vapor phase so that manufacturing of such an electrode having a very large specific surface area is practical and large electrode areas may be manufactured.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photo-rechargeable storage batteryhaving an electron storage property with light different from a solarcell, particularly capable of large areas and having high efficiency,and particularly to a manufacture of a new semiconductor electrodehaving an extremely large ratio of surface area and a large photoreactive site.

Also, the present invention relates to an electrode material for opticalenergy conversion used for a photo rechargeable storage battery, a solarcell or the like.

A photo rechargeable storage battery is a device capable of performingoptical energy conversion and recharging with a unit electrode.

2. Related Art Statement

Hitherto, a photo rechargeable storage battery was investigatedemploying one substance having both semiconductivity and an electronstoring property, but in this case, the energy conversion efficiency andthe electron storing efficiency are low, respectively, and its practicalutilization is still a long way off. As an electrode material, a layercompound semiconductor (intercalation compound semiconductor) and amacromolecular material having semiconductivity were studied. In thiscase, however, in addition to the above various low efficiencies,manufacturing steps become complicated, and it is difficult to put thismaterial to practical use as a solar light device requiring large area.Therefore, it is necessary to develop an electrode having sufficientenergy conversion and storing efficiencies, and to obtain a method ofeasily manufacturing the electrode having large area with simplefabricating steps.

That is, the material capable of putting it to practical use is notfound, since the dissolution of the electrode or the like arises in theintercalation compound. Moreover, in the usual silicon solar cell, it ispossible to make an area of vapor deposition film large, but in theintercalation compound having photo rechargeable property, such amanufacturing method is not established, so that this becomes a largestretch to put in to practical use.

Moreover, a macromolecular material (polythiophene or the like) having asemiconductive property is also known as a electrode material for photorechargeable storage battery, but for the photo rechargeable property,enough efficiency to obtain it, as in the intercalation compound, cannot be obtained. In this way, an electrode material of practical utilityfor a photo rechargeable storage battery has been not yet reported.

Therefore, it is necessary to manufacture an electrode having sufficientenergy conversion efficiency and storage efficiency. Photo-rechargingconsists of two reactions, that is, a reaction of separating photoexcitation carriers in a semiconductor and a reaction of recharging thecarriers. A conventional electrode material is a material having both asemiconductor property and charging capability, so that it is difficultto find or synthesize a material having suitable characteristic from theviewpoint of both of the above considerations.

SUMMARY OF THE INVENTION

The present invention is based on the fact that processes oflight-energy conversion and charging are performed respectively byutilizing different materials, and these materials are composed to forma composite electrode, and then, this composition is performed with fewmicron unit by noting microscopic property of the electrode, therebyobtaining realization of photo-rechargeable property with highefficiency.

Moreover, in order to put it to practical use, it is also necessary tomanufacture the electrode having large area with simple manner. To thisend, a conductive polymer as a charging electrode and a semiconductorperforming light-energy conversion are polymerized with a filter paperas a base material in vapor phase, thereby forming a composite electrodecapable of utilizing respective fibers of the filter paper as anelectrode.

It is an object of the present invention to eliminate the abovedescribed disadvantages of the conventional photo-rechargeable storagebattery.

It is another object of the present invention to provide a highperformance photo-rechargeable storage battery capable of making an areaof the battery large, and a method of manufacturing the same.

It is other object of the present invention to provide a method ofmanufacturing a semiconductor electrode having very large specificsurface area by leading a polymerization of a filter paper as a basematerial in vapor phase, and by manufacturing an electrode on fiber ofthe filter paper and fixing a semiconductor material on the electrode inthe form of fine particle, in the manufacturing process of a solar lightenergy device, and thus to provide a practical storage battery capableof charging with light.

According to the present invention, there is provided aphoto-rechargeable storage battery comprising a composite electrode,said electrode being manufactured by vapor phase-polymerizing apolypyrrole and a gel of polytungustic acid on a filter paper, thiscomposite electrode being utilized as an electrode of the storagebattery.

According to the present invention, in order to manufacture thephoto-rechargeable storage battery capable of being charged with light,on the assumption that the manufacturing method is simple and expensivematerial is not utilized, the composite electrode is manufactured bymaking a conductive polymer as a base. As a method of making efficiencyhigh, in order to manufacture an electrode having large specific surfacearea per unit area, the technique of coating conductive polymer on thesurface of the fiber of filter paper and the technique of adheringmaterial having photo-catalytic property on the conductive polymer filmin the form of a cluster are developed, thereby manufacturing a highperformance photo-rechargeable storage battery, finally.

In an embodiment of the photo-rechargeable storage battery according tothe present invention, there is provided a photo-rechargeable storagebattery comprising a composite electrode, said electrode comprising afilter paper of glass fiber as a base material, a polypyrrole filmcoated on a surface of the filter paper, and an electrode formed bycarrying a gel of poly-tungustic acid on the glass fiber coated with thepolypyrrole film in the form of cluster shape.

According to the present invention, there is provided a method ofmanufacturing a photo-rechargeable storage battery comprising acomposite electrode, the manufacture of said composite electrodecomprising steps of:

preparing a filter paper of a glass fiber as a base material,

immersing a sodium tungstate into the filter paper, and,

introducing a hydrochloric acid as a catalytic vapor into the immersedfilter paper in a gas phase, thereby forming a fine electrode with theutilization of chemical polymerization at the fiber surface, and

repeating these steps, thereby forming an electrode having an extremelylarge ratio of surface area capable of adding different functions withthe use of a vapor phase polymerization.

In a further preferable embodiment of the method according to thepresent invention, there is provided a method of manufacturing aphoto-rechargeable storage battery comprising a composite electrode, themanufacture of said composite electrode comprising steps of:

cutting a filter paper of glass fiber as a base material in an optionalform,

washing the cut filter paper,

coating a polypyrrole film on the surface of the filter paper, and

carrying a gel of poly-tungustic acid on the glass fiber of the coatedthe polypyrrole film on the surface of the filter paper in the form ofcluster shape, thereby forming an electrode.

In the other method of manufacturing a photo-rechargeable storagebattery according to the present invention, the method comprises acomposite electrode, the manufacture of said electrode comprising a stepof producing a polypyrrole electrode, and a step of carryingphoto-catalyst on the polypyrrole electrode, the polypyrrole electrodeproducing step comprising steps of:

cutting a filter paper of glass fiber as a base material in an optionalform,

washing the cut filter paper,

immersing the washed filter paper in solution of oxidizing,

masking the required portion of the filter paper,

inserting the masked filter paper in a desiccator and reducing pressurein the desiccator,

leading pyrrole gas in the desiccator,

leaving it for required hours,

taking out the filter paper from the desiccator,

washing unreacted group, and

the photo-catalyst carrying step comprising steps of:

immersing the thus treated filter paper in solution of sodium tungstate,

masking the required portion of the immersed filter paper,

inserting the masked filter paper in the desiccator and reducingpressure in the desiccator,

leading hydrochloric acid vapor as a reaction gas in the desiccator,

leaving it for required hours,

taking out the filter paper from the desiccator, and

washing unreacted group, thereby forming a composite electrode on thefilter paper by a vapor phase polymerization method.

According to the present invention, as described above, a glass fiberfilter paper is used as a base material, oxidation catalyst ispreviously immersed in the filter paper, the immersed filter paper isinserted in the desiccator, pressure is reduced, and then, theconductive polymeric monomer capable of being charged is lead in thedesiccator. This process makes the conductive polymer polymerized,thereby coating respective fibers of the filter paper with rechargeablepolymer film. As in the same manner, the thus coated filter paper isimmersed in a solution of polytungustic acid, and is treated withhydrochloric acid vapor, so that gel of oxidized tungustic acid becomesparticle shape of order of few μm, and fixed on the fiber coated withpolymer. Therefore, the respective fibers of the filter paper become aphoto-electrode which is formed of fixed gel of tungustic acid havingsemiconductor property, so that the electrode having very large specificsurface area and the photo-reaction site can be manufactured.

In the present invention, respective fibers of the filter paper arecoated with polymer causing rechargeable reaction by polymerizingvaporized polymeric monomer with glass fiber filter paper immersed insolution of oxidizing agent. Moreover, the gel of polytungustic acidhaving particle diameter of few μm and exhibiting semiconductor propertyis fixed. This manufacturing process may be realized with the samefabricating apparatus and the same steps, so that this manufacturingmethod is very simple and the electrode with very large area can easilybe made by using inexpensive filter paper as a base material and bymanufacturing the electrode in vapor phase.

Moreover, in the electrode made by using inexpensive filter paper as abase material and by manufacturing it in vapor phase, respective fibersbecome an electrode, so that the electrode has very large specificsurface area for apparent area and thus the current density per unitarea may be improved largely. Also, polytungustic acid havingsemiconductor property can be fixed in the form of particle havingparticle diameter of few μm, so that light-energy conversion can berealized with high efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A), 1(B) and 1(C) are a step summary view showing manufacturingprocedure of a composite electrode using a filter paper in a vaporphase, an explanatory view of treating the filter paper in a solution,and a diagram of a vapor reaction treating apparatus in a desiccatoraccording to the present invention;

FIG. 2(A) is a microstructure view showing a surface state (condition)of fiber of the filter paper before treating with a scanning electronmicroscope observation;

FIG. 2(B) is a microstructure view of the fiber after polypyrrolecoating treatment showing a state of adhering the polypyrrole conductivefilm on the surface without destroying the structure of the filterpaper;

FIG. 2(C) is a microstructure view of fiber of the filter paperelectrode after a treatment of gel of polytungustic acid showing thatthe gel is diffused and fixed with the particle diameter of few μm;

FIG. 3 is a characteristic view showing a relationship between adischarging current and a lapse of time in the cases of first lightirradiation on the composite electrode according to the presentinvention, of non-light irradiation, and of second light irradiation,respectively;

FIG. 4 is a characteristic view showing a relationship between adischarging current and a lapse of time in case of coating onlypolypyrrole on the filter paper;

FIG. 5 is a characteristic view showing photocharging currents chargedby light, which is obtained by reducing the discharged currents in caseof performing non-light irradiation from the discharge current aftersecond light irradiation;

FIG. 6 is a characteristic view of photocharging currents obtained bysubjecting a comparative examination of an electrode obtained by forminga conductive film having rechargeability of polypyrrole on the filterpaper and forming sol of polytungustic acid (PTA) on the thus formedconductive film and CuFeTe₂ of the intercalation layer semiconductorcompound; and

FIG. 7 is a characteristic view obtained by comparing a cyclicvoltamograph in case of carrying TiO₂ of different photo-catalyst andsol of polytungustic acid on the electrode of polypyrrole filter paperaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the drawings, there is shown an embodiment of a photo-rechargeablestorage battery according to the present invention. As an embodiment, amethod of manufacturing an electrode in a vapor phase with the use of afilter paper is explained with reference to FIG. 1 where valves 5control gas flows. In this embodiment, polypyrrole is selected as arechargeable material, and a gel of polytungustic acid is selected as alight-energy conversion material. The method of manufacturing anelectrode in a vapor phase with the use of a filter paper is concretelyshown in FIG. 1. At first, a glass fiber filter paper 1 is cut out in anoptional form, and is washed with a distilled water. In this example,the filter paper is cut out in 1×4 cm² and immersed in a solution 2 ofoxidizing agent (solution of FeCl₃) so as to form a polypyrrole film onthe surface of the filter paper. Then, the filter paper thus treated ismasked at a required site, inserted in a desiccator 3, and subjected toa reduced pressure treatment by a vacuum pump for few minute. Then,pyrrole vapor generated from pyrrole in liquid phase 4 which is held inthe reduced pressure desiccator to the extent of 70° C., is lead tocommence performing an oxidative polymerization on the filter paper, andleft for a few hours as it is, thereby forming a black polypyrrole filmon the surface of the filter paper. After sufficient polymerization,excess unreacted substance is washed away with distilled water, therebyforming an electrode of polypyrrole treated filter paper.

In this case, polypyrrole is uniformly adhered onto the surface ofrespective fibers of the filter paper, without preventing porosity ofthe filer paper itself. In this way, polypyrrole treated filter paperbecomes an electrical conductor having resistivity of substantially 10³to 10⁴ ohm/cm³ in the surface direction of the filter paper (1×1 cm²).

Then, gel of polytungustic acid is carried and fixed on the polypyrrolefilm. This fixation may be performed in the vapor phase in the samemanner as in the formation of polypyrrole. In this case, a solution 2 ofsodium tungustic acid is used instead of the solution 2 of oxidizingagent and hydrochloric acid is used instead of polypyrrole. The gel ofpolytungustic acid formed on the filter paper is fixed on the fiber ofthe filter paper in the form of fine particles in the same procedure. Aschematic diagram in which the electrode of filter paper is observed bya scanning electron microscope, is shown in FIG. 2. The magnitude of thefine particle can be controlled by changing the concentration of thesolution of sodium tungustic acid.

Since whole manufacturing steps are proceeded in the vapor phase, theregions carrying the reaction substance are masked as described above,so that this embodiment has a merit that the treating steps can simplybe controlled.

FIG. 2 shows the construction of the composite electrode thusmanufactured. In FIG. 2(A), reference numeral 6 is a fiber of the glassfiber filter paper, reference numeral 7 is a fiber of the filter paperafter polypyrrole coating, and reference numeral 3 is a fine particle ofgel of tungustic acid.

This electrode is manufactured in such a manner that the polypyrroleelectrode portion and the carrying portion of gel of polytungustic acidform an interface. Also, schematic diagrams in which the electrodesurface of filter paper is observed by the scanning electron microscope,are shown in FIGS. 2(A), 2(B) and 2(C), respectively.

FIG. 3 shows a graph of discharging property obtained by examining aperformance of a photo-rechargeable storage battery with the use of thiselectrode. This graph shows a comparison of a discharging currentobtained by performing discharge for a reference electrode (Ag/AgClelectrode) after light irradiation for ten minutes with a dischargingcurrent obtained in case of performing non-light irradiation with thesame procedure. In FIG. 3, abscissa shows a discharging time (minutes).In this measuring, aqueous solution of perchloric acid (1 mol/l) is usedas an electrolyte, and xenon light (strength of irradiating light onelectrode surface: 3 W/cm²) having spectral near solar light is used asa light source. As seen from this graph, the discharging current afterlight irradiation is larger than that in the case of non-lightirradiation, so that this shows the feature of having thephoto-rechargeable storage property. The photocharging currents chargedby light, which is obtained by reducing the discharged currents in caseof performing non-light irradiation from the discharge current afterlight irradiation, is shown in FIG. 5. The magnitude of thephoto-charging currents charged by light is an order of few hundreds μA,which is a sufficiently practical value in case of considering a lightirradiation for ten minutes. The method of manufacturing electrodeutilizing the filter paper in the vapor phase may also be applied toanother conductive polymer. TiO₂ which has a many utilizations as aphoto-catalyst, may also be carried in the fine cluster shape in thesame way as the above, so that the present invention is technics havinga wide application range, in addition of application to thephoto-rechargeable storage battery.

FIG. 3 shows a characteristic view showing data of photo-chargingcurrents (FIG. 5) of the composite electrode according to the presentinvention. The characteristic diagram showing photo-charging currentsshown in FIG. 5 is obtained by exhibiting the difference between thedischarging current in the case of non-light irradiation and thedischarging current after the second light irradiation as aphoto-charging current. While the measuring result shown in FIG. 5exhibits the data obtained in case of repeating a following cyclecontinuously:

light irradiation for ten minutes→discharging (discharging after firstlight irradiation)→non-light irradiation→discharging (discharging afternon-light irradiation)→light irradiation for ten minutes→discharging(discharging after second light irradiation)

The curves of photo-charging currents shown in FIG. 5 demonstrate thatthe recharging by the light is realized, since the discharging currentafter the second light irradiation is larger than the dischargingcurrent with non light irradiation (dark discharging).

FIG. 4 shows a characteristic diagram of the discharging current of theelectrode which is formed by coating and polymerizing only polypyrroleon the filter paper, in order to exhibit that photo-rechargeability iscaused only by manufacturing composite electrode.

By performing the same measurement as that shown in FIG. 3, it is foundthat in the electrode having only polypyrrole provided thereon, thedischarging current is decreased with time lapse, irrespective ofpresence of light, so that electrode without gel of polytungustic aciddoes not have the photo-rechargeability.

FIG. 5 is a characteristic diagram of a photo-recharging current of thecomposite electrode according to the present invention, and this currentis obtained as the difference between the discharging current with nonlight irradiation and the discharging current after second lightirradiation.

The comparison between the composite electrode according to the presentinvention and the other electrode is shown in following table 1.

Table 1 shows the relationship among the composition of followingelectrodes, the magnitude of the photo-recharging current(photo-rechargeability), and the photo-voltaic force.

                  TABLE 1                                                         ______________________________________                                        Comparison to other electrodes                                                ______________________________________                                         ##STR1##                                                                     ______________________________________                                    

(1) CuFeTe₂

(2) Gel of polytungustic acid+graphite (film electrode)

(3) Polythiophene

(4) Polypyrrole

(5) Composite electrode according to the present invention

The data shown in the table 1 should be compared with data of otherresearch worker, but the research that the discharging current afterlight irradiation is measured as in the present invention, is not found,so that only the data measured by present inventors are illustrated.

It is found from this table 1, that the photo-recharging current of thecomposite electrode according to the present invention is very large.

FIG. 6 shows a comparison of characteristics of the photo-rechargingcurrent charged by light with the use of both CuFeTe₂ having comparativelarge photo-rechargeability and the composite electrode according to thepresent invention. It is found from FIG. 6 that the composite electrodeaccording to the present invention flows the photo-recharging currenthaving the order of tens times of that of conventional electrode, andthus this composite electrode has a high photo-rechargeability.

Experimental example

The present inventors have tested the photo-rechargeability of seriesobtained by dispersing photo-functional particles into conductivepolymer having recharging property. In conventional electrode,polythiophene is used as a conductive polymer. However, polythiophenehas semiconductivity in the condition that doping is not performed, sothat it is difficult to design an electrode so as to respond it to lighttogether with the photo-functional particles. However, in the presentinvention, polypyrrole which has comparatively metallic conductivity isused as a conductive polymer, and its electro-chemical property andphoto-rechargeable property are tested. Polypyrrole is apt to polymerizeas compared with polythiophene, so that various manufacturing method arepossible and thus the manufacture of composite electrode can be realizedby combining it with the photo-functional particles.

Manufacture of electrode

A filter paper which is applied by solution of FeCl₃ is treated withpyrrole vapor, thereby forming a polypyrrole electrode. In this way,polypyrrole electrode can be manufactured having flexibility andstrength by using the filter paper as basic material. TiO₂ as aphoto-functional particle and sol of polytungustic acid are carried ontothe polypyrrole electrode, thereby forming a composite electrode.

Result

FIG. 7 shows a cyclic voltammogram graph of the polypyrrole filter paperelectrode obtained by dispersing TiO₂ powder and sol of polytungusticacid and carrying them onto the filter paper. It is found from FIG. 7that when TiO₂ powder of various amount of photo-functional particlesand various amount of sol of polytungustic acid are carried onto thepolypyrrole filter paper respectively, various cyclic voltammogramgraphs may be obtained. This means that charge migration between thepolypyrrole filter paper electrode and the photo-functional particles ispresent. Moreover, it is found that the polypyrrole electrode using thisfilter paper increases its reacting region by reflecting porous of thefilter paper, and large current can be obtained as compared withconventional film electrode due to common electro-deposition.

As described above, according to the present invention, high performanceelectrode having very high ratio surface area can be manufactured byapplying a manufacture of electrode in the vapor phase with the use ofthe filter paper as a base material to other devices. Moreover, thesemiconductor can be fixed as a particle, so that the present inventioncan be applied to other devices utilizing a size effect which is notpresent in the conventional semiconductor electrode. This manufacturingtechnic is very general purpose technic, since it can be applied toother semiconductor material capable of manufacturing it with thesol-gel method and other polymer.

Moreover, various different kinds of semiconductor materials may bemixed as a fine particle, so that a photo-electrode having wideabsorption spectrum can be manufactured by forming composite electrodewith the use of semiconductor having different light absorption bands.In this way, the manufacture of electrode in the vapor phase with theuse of the filter paper as a base material is very advantageous inindustry.

What is claimed is:
 1. A composite electrode for a photo-rechargeablestorage battery, comprising:a filter paper of glass fiber as a basematerial; a polypyrrole film coated on a surface of the filter paper;and a gel of polytungustic acid provided on the polypyrrole film in theform of a cluster.
 2. A composite electrode for a photo-rechargeablestorage battery, comprising:a filter paper of glass fiber as a basematerial; a polypyrrole film vapor phase polymerized and coated onto asurface of the filter paper; and a gel of polytungustic acid vapor phasecoated onto the polypyrrole film in the form of a cluster.